The present invention relates to a recording material, and, more particularly, to a pressure-sensitive or heat-developable recording material that uses an electron-donating colorless dye and an electron-accepting compound, and which exhibits an improved color image stability.
Pressure-sensitive or heat-developable recording materials using electron-donating colorless dyes and electron-accepting compounds are disclosed in many patents such as Japanese Patent Publication Nos. 14039/1970 and 4160/1968. The essential requirements that should be satisfied by pressure-sensitive or heat-developable recording materials are: (1) satisfactory color density and sensitivity; (2) the absence of fog (i.e., coloration during storage prior to use); and (3) satisfactory fastness of a colored image. However, none of the products available today totally satisfy these requirements. With conventional recording material of the type that produces a black image, light or other environmental factors tend to cause browning or complete fading of the color image; strong need exists to eliminate this problem.
Many researchers have made studies to develop a method for producing stabilized color images. Three of the methods proposed so far are: (1) addition of a phenolic derivative such as 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (see Japanese Patent Publication No. 43386/1976); (2) addition of a water-insoluble, modified (e.g., rosin-modified) phenolic resin as described in Japanese Patent Application (OPI) No. 17347/1978 (the term "OPI" used herein means "a published unexamined Japanese patent application"); and (3) addition of a terephthalic acid ester as shown in Japanese Patent Application No. 72996/1981. However, the images resulting from the recording materials prepared by these methods are still unsatifactory in terms of stability.